Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$73.33	6.577%	$78.1529	$78.15	$78.15	$78.20
Purchase #2	$150.77	12.493%	$169.6057	$169.61	$169.60	$169.60
Purchase #3	$99.78	9.333%	$109.0925	$109.09	$109.10	$109.10
Purchase #4	$80.79	3.824%	$83.8794	$83.88	$83.90	$83.90
Purchase #5	$105.50	4.375%	$110.1156	$110.12	$110.10	$110.10
Purchase #6	$180.74	3.568%	$187.1888	$187.19	$187.20	$187.20
Purchase #7	$218.41	3.667%	$226.4191	$226.42	$226.40	$226.40
7 purchase totals =	$909.32		$964.4540	$964.46	$964.45	$964.50